The trio sonata form was a popular format for chamber music in the Baroque; among the classical models we have sonatas da camera and da chiesa written in 3 parts by Arcangelo Corelli. For him, the texture was made up of two violins playing together with different parts, with a bass line, the basso continuo which might have been one keyboard instrument, a stringed bass instrument such as the cello, or even a combination of instruments playing the bass line, filling out the harmony. For those listening who are not musicians, the tradition of playing in what the English called a thoroughbass, was “art” of how you read one single line of music, what the cellist might play, for instance, and add your own music on top. Figures, mostly numbers written above the notes, would tell the keyboard, lute, or even gamba player what notes to add above, in a type of tablature shorthand. What is less clear is how free the performer could be in adding to that line, and ensembles today having to make choices about what happens with that line: how many instruments? Do they all play all the time?

In what we now believe may have been arrangements Bach made for the organ, he too dabbled in some trio sonata writing, and of course what’s interesting, is that all three lines are written for one instrument: the organ. Bach wrote these in such a way that the bass line is not written in figures, it’s the pedal line. This meant that his writing for the two treble voices had to be harmonically focused so that there would be no question as to what harmonies were implied. And if needed, the organists hands could always through in an extra note if needed, unlike what would have been possible if the solo instruments were not strings, say an oboe and a flute. Bach refers to the piece specifically as “sonata for 2 keyboards, and pedal.”

BWV 525 is written in the key of E-flat major and is presented in 3 movements (fast-slow-fast). So many trio sonatas appeared in four movement plans, but Bach here instead presents us with three, more aligned perhaps with the idea of an another Italian form, the concerto. Some commentators believe that unlike the other organ trios, this one may have been composed specifically for the organ, and like others from the collection, written as curricular material for Bach’s son, Wilhelm Fridemann. If so, it says nothing of Bach as an actual teacher, but in retrospect, this has to be some of the richest music written for the purpose of teaching technique. Just as other composers may have followed Corelli’s models in their education on how to write a proper trio sonata, here Bach’s actions as a creative genius bare fruit in this sonata, a new type of classical exemplar, which in history, may be considered one of the highest forms the world would see from this age. At the same time, younger composers were already leaving the puzzle-piece design of counterpoint behind in favor for simpler, if not elegant, melodies.

The opening movement presents us with counterpoint, the theme presented first in one line, is then picked up into the second. The two voices then chase one another, with the type of invention that Bach did so well, the theme is in short attractive and is even in such a way that allows for ornamentation.

The middle movement moves into the minor, related key of C minor, that’s undeniably beautiful. Remember, that with a repeat, we believe it was an opportunity to elaborate upon an idea you had already heard. Ad hoc variations, if you will… and the format is the same, an entrance by one voice, that’s then followed by a second, the two when sounding, fitting together like two parts that were designed to come together. In the second half, Bach starts the line in the second voice, giving that part the opportunity to lead their partner. A journey is then taken before we return to the familiar theme from the first half; it’s filled with visits to chromatically jeweled places, which is somewhat reminiscent of the “development” section in the Sonata-Allegro form that would dominate so much music from the classical era.

The last movement, in 3/4 time, is a happy affair, again written in binary form. Again, as in the 2nd movement, the top voice leads in the first half, the second voice leads in the second. The format is again the same, The two lines joined as if in a canon, but displaced by by harmony, not unlike what Bach provided as a guide in his two- and three-part inventions for solo keyboard. Here that application of counterpoint is elaborated upon, borrowing the ideas and stylistic devices made popular by other composers.

If you look at the handwritten facsimile linked above, it’s interesting to see the practical means by which Bach recorded the music onto paper, not a bit of the paper was wasted, with the last ideas being fit almost as footnotes into the bottom of a page, so that a new fresh page would not be wasted.

Little needs to be done to re-write this piece (and other other organ trio sonatas) for other instruments since the lines are very simple (single voices), if anything. If the pedal line is to be interpreted as a basso continuo, then yes, figures can be added to indicate what harmonies might be played. The range of the lines may also be altered, to fit the compass of instruments. Several ensembles have made such an arrangement, and they have chosen the key of G major, which aside from ranges, is a simpler key to play on strings and on wind instruments. I also think the character of the piece fits well with the key of G, a happy, sunny key.

In 1994, the then fresh ensemble known as the Palladians recorded this trio sonata for violin, recorder, and basso continuo (lute and gamba). These instruments, different in sound and in how they make sound, are an excellent choice in expanding the expressive potential of the two melody lines, while also offering a clearer contrast between them. On repeats, however, the Palladians do not capitalize upon doing things too differently than the first time around in the binary movements.

London Baroque's recording for BIS offers us a version written for the ensemble familiar to Corelli's sound world, two violins and continuo. While never extrovert in their playing, they interpret it well and take some small leaps of fancy in the repeats in BWV 525.